This invention relates to certain trialkyl and triaryl organotins and their dissemination in a continuous and controlled manner into water courses infested with mosquito larva and other susceptible aquatic pest life. Mosquito larva develops through morphogenetic stages in water, emerging in time as adults capable of transmitting dreaded diseases which include encephalitis, malaria, yellow fever, and the like, as well as creating a nuisance to man and man's domestic cattle by their proclivity towards biting and other annoyances. Similarly, other insecta, such as flies of the Simulium family, spend their larval stages in water, emerging as adults capable of transmitting onchocerciasis, a dreaded parasitic disease manifested as blindness in exposed human populaces. Snail hosts of parasitic trematodes, as well as the trematode larva, likewise, dwell in water and can similarly be controlled using the invention described in this specification.
Insects and other bearers of disease are normally and conventionally destroyed through treating the infested waters with larvicidal agents or saturating the air with sprays, fogs, droplets, etc., of specified toxic substances. It is well known that the conventional methodology provides but temporary relief, while of necessity, the use of toxicant concentrations has, as a rule, a significant detrimental ecological effect on non-target organisms, soil, air and water. As described in the monumental text by Cardarelli, 1976, and is now well known to the pesticide formulation and used in the art, through the incorporation of select pesticides in select polymeric matrices, it is possible to cause a slow-long duration release of ultralow concentrations of said pesticides in the pest-infested environment with efficacious benefit and much reduced environmental impact. When target organisms are continuously exposed to very low toxicant concentrations, such concentrations being far too small to materially affect insect control, the gradual accumulation of such agents in the pest body leads to a chronic manifestation of intoxication and eventual mortality.
Slow release toxicant compositions, such as those taught in U.S. Pat. Nos. 3,639,583 and 3,417,181, rely upon release being affected through the now well-known and well-understood diffusion-dissolution mechanism. It is taught in said patents that release is critically dependent upon the binding polymeric matrix being a solute for the organotin classes used. The binder matrix is a vulcanized or a partially vulcanized elastomer. However, it is well known that generally organotins totally lack solubility in thermoplastic materials and, thus, the diffusion-dissolution process cannot be established.
In other inventions, it has been taught that the pesticidal agents such as organophosphorus class insecticides will similarly release from solute matrices, especially from elastomers. U.S. Pat. No. 3,590,119 is an example of this teaching.
Many mosquito larvicides are known and used in both the conventional sense as well as in controlled release methodologies such as microencapsulation. Among others, Boike et al has shown in examining 23 different organotins in solute elastomer formulations, that they are not effective against the mosquito under practical use situations due to the presence of natural organic substances common to water courses. Said organic materials rapidly absorb organotin molecules essentially removing them from mosquito larva contact.
U.S. Pat. No. 4,012,221 has taught that an elastomer insoluble toxicant, if said toxicant is highly water soluble and is present in relatively high matrix concentrations, can be made to release from said elastomer in excess of 75 parts by weight of toxic per 100 parts of elastomer.
U.S. Pat. No. 3,705,938 teaches that several organophosphorus-type insect adulticides can be incorporated in a laminated polyvinylchloride structure, wherein no agent solubility exists, and caused to move continuously through said plastic structure to said plastic surface through a volatility mechanism wherein the medium of release is air. Such constructions require the use of a third phase material such as a plasticizer to effect toxicant movement.
In pursuance of the invention described herein, it has been discovered that unlike conventional pesticides, specific organotin chemicals act through a hitherto unknown mechanism to effect mosquito and snail mortality. As is well known to the state of the art, organophosphorus, carbamate, halogenated hydrocarbon, and other organic materials affect mortality in insects by interference in vital enzyme systems. It is further well known that this mode of intoxication leads to the unwanted development of resistance to said chemicals through evolutionary processes. In contrast, organotin formulations described herein effect mortality through hitherto undiscovered physiological mechanisms that cannot induce tolerance in the target species.